Method of treating waste-activated sludge using electroporation

ABSTRACT

A system that allows the flexibility of primary and secondary treatment of municipal sludge, paper-pulp sludge, animal and plant waste, whereby the treatment thereof via electroporation may be used either as the primary dewatering treatment, secondary dewatering treatment, direct WAS-treatment, and combinations with other conventional dewatering techniques, in order to provide the municipal treatment plant, or the paper-pulp treatment plant, with the most cost-effective and efficient system as possible. The electroporated-treated sludge releases hitherto unreleased biosolids exiting from the PEF-electroporation system, which are returned to aeration tanks. The electroporation process causes the release of intracellular dissolved/organic matter, which is used as “food” for the bacteria of the aeration tanks.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of application Ser. No. 09/612,776, filed Jul.10, 2000, which is a continuation-in-part application of applicationSer. No. 09/468,427, filed on Dec. 21, 1999, which is incorporated byreference herein in its entirety, which is a continuation of applicationSer. No. 09/229,279, filed on Jan. 13, 1999, now U.S. Pat. No.6,030,538, which is a continuation-in-part of application Ser. No.08/934,548, filed on Sep. 22, 1997, now U.S. Pat. No. 5,893,979, whichis a continuation-in-part of application Ser. No. 08/552,226, filed onNov. 2, 1995, now U.S. Pat. No. 5,695,650.

BACKGROUND OF THE INVENTION

In parent application Ser. No. 09/468,427, there is disclosed a systemand method for dewatering and treating waste-activated sludge (WAS)emanating from municipal waste, or pulp-waste from a paper mill, as wellas treating animal and plant waste. In that application, the method forbreaking down the WAS is to subject the WAS to electroporation, whichincorporates nonarcing, cyclical high voltages in the range of between15 KV and 100 KV, which break down inter-cellular and intracellularmolecular bonds, to thus release inter-cellular and intracellular water,whereby the WAS is rendered inactive and greatly reduced in mass.

In said above-noted copending application, the apparatus and methoddisclosed therein, while capable in certain circumstances of being aprimary municipal-sludge treatment, its intended and main objective wasto use it as a secondary treatment to previously-dewatered municipalwaste sludge. It is the goal of the present invention to adapt themethod and apparatus of said copending application serial No. 09/468,427into a main, primary treatment of municipal waste sludge.

In a previous (Phase I) project, it has been demonstrated the laboratoryfeasibility of pulsed electric field (PEF) for disrupting the biomass inwaste activated sludge (WAS) derived from municipal wastewatertreatment. While there was no significant increase in the solids contentof dewatered sludge, the quantity of WAS needing disposal was estimatedto be significantly reduced.

Encouraged by the Phase I results, a pilot plant for testing at one ortwo wastewater treatment plants that generate WAS has been developed. Ithas been decided that a pulsed electric field (PEF) system that couldhandle 0.5 to 1.0 pgm WAS feed be designed. This requires an 8 kw powersupply capable of generating 30 kV and pulse generator capable ofhandling 50 amp peak, current, bi-polar pulses, square wave, 10 μs pulsewidth, and 3000 pulses/second (pps).

SUMMARY OF THE INVENTION

It is the primary objective of the present invention to provide a methodand apparatus for dewatering municipal waste sludge, paper-pulp wastesludge, animal and plant waste, using electroporation for the primarytreatment of the sludge.

It is also a primary objective of the present to provide such a systemthat will allow flexibility as to the primary and secondary treatment ofmunicipal sludge, paper-pulp sludge, animal and plant waste, whereby thetreatment thereof via electroporation may be used either as the primarydewatering treatment, secondary dewatering treatment, directWAS-treatment, and combinations with other conventional dewateringtechniques, in order to provide the municipal treatment plant, or thepaper-pulp treatment plant, with the most cost-effective and efficientsystem as possible.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be more readily understood with reference to beaccompanying drawings, wherein:

FIG. 1 is a schematic showing the electroporation system as used as asecondary dewatering treatment;

FIG. 2 is a schematic showing the electroporation system used inconjunction as a primary dewatering treatment in accordance with thepresent invention;

FIG. 3 is a schematic showing the electroporation sub-system for use indewatering municipal, paper-pulp, animal and plant waste sludges; and;

FIG. 4 is a schematic diagram showing the overall apparatus of thepresent invention incorporating the electroporation sub-system for useas a primary or secondary dewatering treatment;

DETAILED DESCRIPTION OF THE INVENTION

The original concept for the pulsed-electric field (PEF) effect usingelectroporation was to dewater the previously-dewatered sludge. However,additional PEF data on a paper plant sludge has indicated that the bigPEF effect from electroporation of WAS occurs at higher energy levels(e.g., 100 J/mL; or 400 k Wh/ton (DS) for feed at 6 percent solids),whereby cells are disrupted. The result is inactivation of cells,breakage of cells and release of some intracellular dissolved/organicmatter and typically a worsening of flocculation and dewatering.Therefore, a more effective way of using this process is to recycle allof the PEF-treated sludge back to a aerobic bioreactor to utilize thesludge as food; that is, it has been discovered that thePEF-electroporation effect on disrupting the cellular units of the WAShas been to release intracellular dissolved/organic matter. Thisintracellular dissolved/organic matter is just the type of ideal “food”upon which the aerobic bioreactor flourishes. Thus, returning thisreleased intracellular dissolved/organic matter back to the aerobicbioreactor will increase the BOD load on the bioreactor, and will thusreduce the quantity of WAS by up to about 50 percent. The flowsheet forthis scenario is shown in FIG. 2. Thus, it is now practical to employthe PEF-electroporation system as not only a secondary system fortreating previously-dewatered sludge, but also to employ it as a primarysystem, as described hereinbelow.

Referring to FIG. 1, there is shown the schematic for using thePEF-electroporation system as a secondary treatment forpreviously-dewatered sludge, as disclosed in Applicant's copendingapplication serial No. 09/468,427. In FIG. 1, the wastewater isdelivered to the primary treatment, aerobic-reactor tanks 10, and to asecondary clarifier 12. From there, the WAS is delivered to thePEF-electroporation system 14 of the invention for deactivating the WASto make it a Class “B” biomass for easier disposal. The biomass is thensent to a belt press 16 for further processing and disposal.

Referring now to FIG. 2, there is shown the flow chart of the presentinvention for employing the PEF-electroporation system as part of theprimary treatment. In this system, the biosolids exiting from thePEF-electroporation system 14 are returned to the aeration tanks 10,since, as explained above, the PEF process causes the release ofintracellular, dissolved organic matter, which is used as “food” for thebacteria of the aeration tanks. This “food” not only is further treatedin the aeration tanks via aerobic digestion, but actually causes theaerobic digestion process in the aerobic tank itself to be acceleratedfor the same amount of oxygen supplied.

A practical problem with the system of FIG. 2 is that the PEF throughputneeds to be of the same order of magnitude as the WAS disposal rate inorder to see a noticeable effect of PEF on WAS reduction. For thisreason a 1.8 ton (DS)/day PEF system has been chosen as a pilot plant.With such a system, a WAS reduction of 0.9 ton/day on a dry basis or 7.5tons/day on a filter press cake (at 12 percent solids) basis may beachieved. In terms of thickened sludge (at 2 percent solids) basis, thistranslate to elimination of 45 tons/day needing to be flocculated anddewatered. This will require PEF treatment of 15 gpm WAS at 2 percentsolids.

One way to reduce the cost of the pilot plant, which is driven by thePEF power supply and pulser cost, is to pre-thicken the WAS. Therefore,a 15 gpm rental centrifuge 18 is used for pilot testing. It is estimatedthat this will produce a 5 gpm feed for the PEF reactor at a solidscontent of 6 percent. Such a feed can be handled by a Moyno pump. Thefeed streams to the centrifuge and the PEF units are represented asStream Nos. 10 and 11, respectively in FIG. 2. However, in practicalapplication such as centrifuge may not be necessary.

PEF Power Supply and Pulser Design

The conceptual design of the power supply and the pulse generator(pulser) for the system of FIG. 2 is shown in FIG. 3. This figure showsfour chambers 20 in series, although two chambers also can be used ifthe pulse rate is increased. The specifications for the two-chamberdesign are shown in Table 1. The design requires a 35 kW input powersupply 22 (32 kW continuous output) delivering 30 kV. The pulsegenerator 24 is 200 amp maximum current and a pulse rate of 4,000 hz.(maximum).

TABLE 1 Pilot Plant PEF Power Supply, Reactor, and Pulser Chambers GapDistance D (cm) 1.2 Chamber 1 Number of chambers in use 2 FlowConditions Flow rate (ml/s) 315 PEF Parameters Voltage to apply (kV) 30Rep-rate (pps) 3342.254 Pulse duration (μs) 4 Physical PropertiesConductivity (S/m) 0.2 Density (g/cm³) 1 Specific Heat ([J/(g · ° C.)]4.18 Viscosity (Pa · s) 0.0100 Dosage Level Electric Field Strength(kV/cm) 25 Total Treatment Time (μs) 80 Number of pulses per chamber 10Temperature Change Temperature increase per pair of chamber (° C.)11.962 Related Information Residence Time (s) 0.00299 Flow Speed (cm/s)401.070 Energy Consumption (J/ml) 100 Estimated Power requirement (W)31500 Reynolds Number 4010.705 Pulse Generator Current 78.5

The actual sludge handling system and the associated instrumentation isshown in FIG. 4. A detailed list of specifications is provided in Table2. Tank T1 holds up to 100 gallons of untreated feed material, deliveredthrough valve V1 from the centrifuge. A mixer is provided for blendinginfeed material. A bottom drain allows disposal to sewer at the end of atest run. Valve V4 is provided for withdrawing a sample for analysis.Material leaves T1 through V2 and a strainer to a variable-speedprogressing cavity pump, which can flow from 0.5 to 5.0 gallons perminute. The tank, pump mixer and associated valves are mounted to one42-inch square skid for transport purposes. The feed leaving P1 passesthrough quick-connect fittings to a reinforced hose to the reactor.

The PEF-electroporation reactor subsystem includes a power supply, pulsegenerator and pairs of treatment chambers as described above withreference to FIG. 3. These would be mounted to a skid, along withassociated valves V5, 6 and 7. Quick-connect fittings and hose conveythe treated material to valves on the outlet tank skid. Valves V12 and13 permit the treated material to be recycled back to T1. Valve V8permits the treated material to enter tank T2, of 100-gallon capacity.As with T1, a mixer, a sample port and a bottom drain are provided. TankTank T2, pump P2, mixer M2 and associated valves are mounted to anotherskid. Treated material leaving through V10 leads to transfer pump P2.Valve V15 is a globe style for adjusting the flow rate through V14 totank T1. Valve V13 allows treated material from T2 to return to T1,assisted by P2, to increase treatment time.

The P2 pump is used to return the treated sludge to the biotreatmentplant, aerobic tanks, when the PEF-electroporation system is used as aprimary system, or optionally to filter press, if desired, when thePEF-electroporation system is used as a secondary treatment.

Safety logic has been incorporated as follows. Level control L1 willclose V1 to prevent overfilling T1, with subsequent spillage. Levelcontrol L2 will shut down P1 and the power supply when the liquid levelbecomes too low. Level control L3 will shut down P1 and the power supplywhen tank T2 becomes full, to prevent spillage.

TABLE 2 Sludge Handling System Specifications Description Supplier QtyInlet Tank T1 100-Gal carbon steel jacketed mixing tank 1 Buckeye Fab. 12-inch PVC, Schedule 80 90-Deg. elbow, 806-020 (bypass in) HarringtonMixer, 1 C-Clamp mount direct drive, ¼ HP, 400-250-DD-ED Harrington 2Union ball valve, 2-inch socket, 1001020 Harrington 1 Strainer, 2-inchclear PVC, RVAT108 Harrington 1 Replacement screen, PVC Harrington 12-inch PVC, Schedule 80 pipe, 800-020, 20 feet length Harrington 22-inch PVC, Schedule 80 90-Deg elbow, 806-020 Harrington 2 Quickdisconnect, Part F, 2-inch, polypro., FPP-020 Harrington 2 Quickdisconnect, Part C, 2-inch, polypro., CPP-020 Harrington 100 ft Hose,PVC standard duty, 2-inch, 110P-020 Harrington 10/pack Hose clamps,3-inch, H-44SS Harrington 1 Bulkhead fitting, ½-inch PVC BF10050SXTHarrington 1 Ball valve, ½-inch socket, 107005 Harrington 1 Elbow,90-degree, ½-inch Sch 80 Pvc, 806-005 Harrington 1 Level control, highto shut feed valve, LV751 Omega 1 Level control, low to shut off pump P1and Powr supply, LV751 Omega 1 Solid state relay for feed valve,SSR240AC10 Omega 1 Solid state relay for pump and power supply,SSR240AC25 Omega 1 Feed Valve V1 Quick disconnect, Part F, 2-inch,polypro., FPP-020 Harrington 1 Quick disconnect, Part C, 2-inch,polypro., CPP-020 Harrington 1 Union ball valve, 2-inch, 1001020Harrington 1 Electric actuator, 2085020 Harrington 1 Process Pump P1Pump, 5.0 down to 0.5 GPM, 35 psi, Moyno Buckeye Pump 1 Direct Currentcontrol for pump, NEMA 4 enclosure Buckeye Pump 2 Hose nipples,polypro., 2-inch, HNPP-020 Harrington 2 2-inch PVC, Schedule 80 tee,801-020 Harrington 1 2-inch PVC, Schedule 80 pipe, 800-020, 20 feetlength Harrington 2 2-inch PVC, Schedule 80 90-Deg elbow, 806-020Harrington 2 Reactor Connections Quick disconnect, Part F, 2-inch,polypro., FPP-020 Harrington 2 Quick disconnect, Part C, 2-inch,polypro., CPP-020 Harrington 1 Union ball valve, 2-inch socket, 1001020Harrington 2 2-inch PVC, Schedule 80 socket tee, 801-020 Harrington 2Reducing bushing, 2-inch by ½-inch thread, 838-247 Harrington 2 ½-inchby 1-1/2-inch long PVC Schedule 80 nipple, 882-015 Harrington 2 Unionball valve, ½-inch threaded, 1001005 Harrington 1 ½-inch PVC Schedule 80threaded tee, 805-005 Harrington 2 Reducing bushing ½-inch to ¼-inchthreaded, 839-072 Harrington 1 Pressure gauge with guard, 0-60 psig,GGME060-PP Harrington 2 Tube adapter, ¼-inch MPT to ¼-inch tube,4MSC4N-B Parker Outlet Tank T2 1 100-Gal jacketed carbon steel tank withlegs, 2-in outlet Buckeye Fab. 1 2-inch PVC, Schedule 80 90-Deg elbow,806-020 (inlet) Harrington Union ball valve, 2-inch socket 1001020Harrington 3 Quick disconnect, Part F, 2-inch, polypro., FPP-020Harrington 3 Quick disconnect, Part C, 2-inch, polypro., CPP-020 3Harrington 4 2-inch PVC, Schedule 80 90-Deg elbow, 806-020 Harrington 22-inch PVC, Schedule 80 socket tee, 801-020 Harrington 3 2-inch PVC,Schedule 80 threaded tee, 805-020 Harrington 2 2-inch by 6-inch PVC,Schedule 80 nipple Harrington 1 Mixer, C-Clamp mount direct drive, ¼ HP,400-250-DD-ED Harrington 1 ½-inch by 2-inch PVC, Schedule 80 Harrington1 Ball valve, ½ inch socket, 107005 Harrington 1 Elbow 90-degree, ½-inchSch 80 PVC, 806-005 Harrington 1 Level control, low to shut off pump P1and Powr supply, LV751 Omega 1 Solid state relay for pump and powersupply, SSR240AC25 Omega Outlet Tank Pump Pump, 5 GPM 20 feet of head,centrifugal 1 Buckeye Pump Motor starter, NEMA 4 with thermal unit 1C.E.D. Hose nipples, polypro., 2-inch, HNPP-020 4 Harrington 1 Glovevalve, threaded, PVC, 2-inch, 1261020 Harrington Product Pump P2 Pump, 5GPM 20 feet of head, centrifugal 1 Buckeye Pump Motor starter, NEMA 4with thermal unit 1 C.E.D. Sealtite, ½-inch lot C.E.D. Wires, cords lotC.E.D. Skids 42-inch square, metal, fork lift entry four sidesInstrumentation Oscilloscope, storage, two inputs, 100 MHz, 1 printerinterface Tektronix 1 Current sensor, 0.01 Volt/Ampere, 100 Amp. max.Pearson Electr. 1 Clamp-on flowmeter, 2 to 12-inch pipe, 4-20 ma outputControlotron 1 Voltage sensor, 60 Kilovolt, 1000 v/1V, Type PVM-1 NorthStar Resch 1 Printer, Epsom jet Model 740, Part No. C257001 parallelport ADS Systems 1 Centronics-type paraller printer port cost, EpsomF2E020-06 ADS Systems 1 ea. Type K thermocouple readout, Omega DP45KF +SB45 Omega 2 Type K thermocouple, 304SS sheath, 1/8-in. dia.,KQSS-18G-12 Omega 1 Conductivity and pH meter, 0-200 μS, 0-14 pH,P-19651-20 Cole-Parmer 2 Conductivity and pH flow-through cell,P-19502-42 Cole-Parmer Alternative clamp-on flow meter, Omron FD-303 +FD-5 sensor for ¼-in. to ¾-in. pipe + FD-5000 sensor for ¾-in. to 12-in. pipes.

While a specific embodiment of the invention has been shown anddescribed, it is to be understood that numerous changes andmodifications may be made therein without departing from the scope andspirit of the invention as set forth in the appended claims.

What we claim is:
 1. A method of treating waste-activated sludgecontaining intra-cellular water molecules contained in molecularcellular units of the waste sludge, comprising: (a) pumping the wastesludge into a dewatering apparatus for separating waste-activated sludgetherefrom; (b) directing the waste-activated sludge to anelectroporating station; (c) electroporating the waste-activated sludgefor destroying at least most of the individual cellular units of thewaste-activated sludge in order to release the intra-cellular watermolecules A contained therein; and said step (c) causing massivedisruption of the cellular matter, allowing for the release of bound aswell as intra-cellular liquids and intracellular dissolved/organicmatter; further comprising after said step of electroporating: (d)directing the released intracellular dissolved/organic matter to anaeration tank for supplying food to bacteria of said aeration tank forperforming aerobic digestion thereon, whereby the intracellular,dissolved organic matter is used as food for the bacteria of theaeration tank.
 2. The method according to claim 1, wherein said step ofelectroporating comprises subjecting the waste-activated sludge to avoltage between 15 KV. and 100 KV.
 3. A method of treating waste sludgefrom an aeration tank for perforating aerobic digestion, comprising: (a)treating the sludge in an electroporating process that releasesintracellular dissolved/organic matter from said sludge; (b) directingbiosolids and the released intracellular dissolved/organic matter fromsaid step (a) to an aeration tank for performing aerobic digestionthereon, whereby the intracellular, dissolved organic matter is used asfood for the bacteria in said aeration tank, whereby the aerobicdigestion process is accelerated thereby for the same amount of suppliedoxygen.
 4. The method according to claim 3, further comprisingalternatively directing the sludge directly to a further dewateringprocess.